Alan Titchmarsh solves your gardening problems

Here, exclusively for subscribers, Alan Titchmarsh offers organic solutions to problems with your roses, acers and jasmine, he tackles box caterpillars, vine weevils, plants not flowering, leaves turning brown and much more.

Why, oh why, won't my dieramas do? Ros Palmer

Alan Titchmarsh says:

Oh I do sympathise! I have had the same problem, but discovered that the best place for dieramas is really well-drained soil in a sunny spot. A gravel mulch seems to help, too. Make sure that you have a vigorous, healthy plant at the start and plant it out in April so it has a chance to establish itself before winter. Soggy soil in winter and summer drought will both see it off, and it doesn’t like being moved, so if you think you’ve found the right spot, be patient!

I have a well-established shrub rose. This year, half the growth looks like a wild rose and the other half normal. Should I cut out all the wild bits? Denise Taylor

Alan Titchmarsh says:

Rose bushes produced commercially are always raised by ‘budding’ a chosen variety on to a wild rose rootstock, usually Rosa laxa. Any shoots that come from that part of the plant – below the spot where the variety was budded on to the rootstock – will be of the briar itself. They are referred to as suckers and need to be pulled off, rather than cut off so that they do not take over from the variety itself. If they are too strong to be pulled off then snip them off as close to their point of origin as you can.

The leaves on my acer are going brown and drying out. What should I do? Mel Collins

Alan Titchmarsh says:

Japanese maple leaves are very susceptible to loss of moisture – especially the cut-leafed varieties. This may be caused by drying winds, scorching sun and/or dryness at the roots. Try moving your plant in autumn to a more sheltered spot in dappled shade and make sure – particularly during the early stages of establishment – that the soil around it is not allowed to dry out completely. Acers don’t need a boggy paddy field, but they do enjoy a decent supply of moisture to keep that mass of frilly leaves fully hydrated.

My Jasmine plants look healthy but they don't have any flowers. What can I do? Helene Huggett

Alan Titchmarsh says:

Check that your jasmine is receiving enough sunshine on its shoots to ripen the wood and encourage flower production. Give it a boost twice a year – once in March and again in June – with a good sprinkling of rose fertiliser, scattered on the soil around the foots and watered in. The potash and magnesium this fertiliser contains will give it some encouragement to flower.

We have a couple of well-established camellias in large pots which have never flowered. Any advice? Viv & Hugh Nickless

Alan Titchmarsh says:

Your camellias are probably hungry! Repot them in spring, preferably into a larger container of ericaceous (lime-free) compost. If they are already in large pots, they have probably filled them with roots and are starving. Pale-green foliage is a reliable indicator. Get them out of the pots, scrape away some of the old compost along with some of the outer roots and replace the old compost with fresh. A dilute ericaceous liquid feed once a fortnight from March to September will help them. Snip away between a quarter and a third of the shoots after repotting to help reinvigorate the plants.

Vine weevils are destroying my plants. What is the best way to get rid of them and is there any way to prevent them? Gary Lindsay

Alan Titchmarsh says:

Vine weevil is a heartbreaking pest to encounter, not least because the damage often goes unnoticed until the plant collapses due to the roots being eaten away. Always use fresh and sterile compost when potting up plants, as well as clean containers. Water susceptible plants with a biological nematode vine weevil control such as Nemasys, strictly in accordance with the instructions on the product.

Some of the leaves on my containerised apple tree are coated in white stuff then curling up and dying. What's wrong with it? Deb

Alan Titchmarsh says:

Your potted apple tree is suffering from mildew – a fungus disease that is especially prevalent when trees are under stress, which usually means they are dry at the roots. Make sure that there is plenty of air circulating around the plant (thinning out overcrowded stems will help) and try to keep the compost gently moist at all times. Apply dilute liquid tomato feed once a week between April and September to build up the plant’s ability to grow through the attack.

I have a severe infestation of box caterpillar. Should I pull it all up? Roland Backhouse

Alan Titchmarsh says:

Don’t get rid of your plants just yet! Well fed and watered they will eventually recover provided you take other precautions such as hanging up a box moth trap and spraying three times during the growing season (when each of the three generations of box caterpillars emerges) with a solution such as Top Buxus Xen Tari. Spraying the bushes with a sharp jet of water will also help them to shed the caterpillars which will be eaten by birds.

• Alternatives to box

There is a white froth on some of our plants, is this harmful? Amanda

Alan Titchmarsh says

This is ‘cuckoo spit’, and each collection of froth will be protecting a single frog hopper insect. They do little damage to plants but the spit is unsightly. Squirt them with a sharp jet of water from a hosepipe to remove them.

I have had no gooseberry sawfly for years. This year, I covered my gooseberries with netting to keep off birds, but a week later, all the leaves had gone and there were caterpillars all over the bush. What should I do? Bob Sparkes

Alan Titchmarsh says:

The birds might well have been helping by eating the gooseberry sawfly! It will be worth uncovering the plants. If there are too many caterpillars to hand pick, try spraying with the biological nematode caterpillar control Nemasys in May, when attacks are usually first noticed.

• How to grow gooseberries

Can you suggest any chemical-free solutions to black spot, rust and other fungal disease problems in roses? Samantha Merridale

Alan Titchmarsh says:

Roses almost always succumb to these diseases when they are under stress and that usually means they are dry at the roots. So…make sure that the soil in which they grow is moisture retentive. Clay soils are traditionally enjoyed by roses for that reason. Beef up lighter soils with plenty of organic matter – well-rotted compost and manure – which will help hold on to moisture. In prolonged dry spells, soak the soil – especially around newly planted roses – using a hosepipe. Varieties with delicate foliage are particularly susceptible, so choose roses with thick, leathery leaves and you will find they are much more likely to resist these diseases.

• Trouble-free roses

Why are the leaves on my potted camellia turning brown? Karen Johnstone

Alan Titchmarsh says:

This is most frequently caused by scorching sunshine, though there are also fungus diseases that cause leaf browning. In every case, pick off the affected leaves and dispose of them. ‘Sun scald’ is caused when the leaves are subjected to overly strong sunshine – camellias grow best in dappled shade. They also need lime-free ‘ericaceous’ compost when being grown in a container, but alkaline soil conditions cause yellowing rather than browning of the leaves. Dryness at the roots is another cause of leaf browning. In short, make sure your container-grown plant is shaded from bright sunshine and that the compost is never allowed to dry out completely.

My Viburnun tinus has branches that suddenly turn brown and die. Why? Jemima Cole

Alan Titchmarsh says:

This is a common problem and there are several possible causes. Some form of mechanical damage may be responsible – a cut to the stem, damage by a pest or some such physical occurrence. The simplest thing to do is to snip out the affected stem, well back into healthy tissue. Viburnum tinus is a vigorous plant and will soon recover from the attack. One or two fungus diseases may also be responsible. Good drainage at the roots and good air circulation around the plants will help to prevent attacks. In every case, cut out and dispose of infected tissue. The plants also benefit from an occasional feed with blood, bone and fishmeal.

• Best viburnums to grow

How should I deal with peach leaf curl? Gill Hollick

Alan Titchmarsh says:

Peaches in a greenhouse are seldom affected but those outdoors are likely to succumb every year. You will find that if you rig up a sheet of polythene above wall-trained trees in January, to act like a curtain, attacks will be much reduced. Remove any leaves that are affected and dispose of them – do not put them on the compost heap where the fungal spores can survive. Spray the unfurling leaves with an organic foliar feed every couple of weeks, which will improve the plant’s overall strength. As you have noticed, as the season progresses the leaves cease to be attacked.

My broad beans were riddled with chocolate spot and blackfly. How can I prevent this? Marion Hayman

Alan Titchmarsh says:

Broad beans are frequently attacked by a fungus disease called chocolate spot. It is prevalent in damp weather and where plants are growing too close together which results in poor air circulation. Make sure the site you choose is in full sun and that the plants have room to grow without touching one another – space them about 30cm apart. Don’t compost any affected plants, don’t save seed from affected plants, and change the place in which you grow your broad beans each year. Blackfly (aphids) love the tender tips of broad beans, so once the plants are 45-50cm high, pinch out the shoot tips to allow the plants to concentrate on developing their beans and to remove the tender tissue.